My U.S. Pat. No. 5,392,744, issued on Feb. 28, 1995 and entitled "Precombustion Chamber For a Double Overhead Camshaft Internal Combustion Engine", describes a pre-combustion system utilizing a central pre-combustion chamber. When this system is combined with a radial valve cylinder head design, an overall improved combustion system for an internal combustion engine can be achieved. However, I believe that two modifications in pre-combustion chamber design can further enhance the operation of an engine; improving its efficiency for increased engine power with reduced fuel consumption and emissions. The first modification involves reducing heat losses through a novel insulation arrangement and such modification is the subject of my two co-pending patent applications identified as P-371 and P-376, each of which is entitled "Insulated Pre-Combustion Chamber". The second modification concerns the pressure losses incurred by the air entering the pre-combustion chamber and the products of combustion and fuel leaving the chamber.
In this regard, it is believed that the flat inside bottom surface of the pre-combustion chamber on which the four transfer passages discharge gases, being a sharp-edge in part, create turbulent eddies because it is a non-aerodynamic design. As a result, the pressure losses incurred in the chamber are increased and reduce the air flow into the chamber during the compression stroke. Worse still, the outflow losses are particularly affected. Since pre-combustion chambers are designed to operate at high temperatures so as to efficiently aid the initiation of ignition and continuation of combustion, it is desirable that its volumetric efficiency be as high as possible and that the air within the chamber at the moment of fuel injection possess the highest energy level. This is necessary because the auto-ignition process of the fuel is a time-temperature function, that is, with the highest temperature, the lowest time. The time delay, therefore, between the beginning of injection and ignition is referred to as "ignition delay". Since during ignition delay, fuel continues to be injected up to and past the moment of ignition, it follows that the longer the ignition delay, the more fuel that is injected during its time span, the more fuel that burns practically simultaneously and immediately following the point of self-ignition. This early ignited mass of fuel produces a sharp chemical noise or detonation, which is also aided by mechanical vibrations incited in the pre-combustion chamber walls and surrounding engine structure. In reality, not much of the energy is transmitted to the piston, crankshaft, and engine block because the heavy explosion is dampened from immediate passage into the main combustion chamber by the transfer passages. The practically simultaneous self-ignition of all the fuel present also increases the NO.sub.x emissions because of all the fuel burnt at this time. In other words, the fuel that has entered the pre-combustion chamber lastly prior to ignition has not mixed well and produces highly localized high-temperature spots that are the genesis of NO.sub.x. Hydrocarbons, particulate, and smoke are also produced by these high temperature spots of uncontrollable combustion, since some of this lastly injected fuel may not find air to combust and, instead, pyrolyses as carbon soot which may or may not be burned later within the main combustion chamber. The requirement of this process is, therefore, to reduce the ignition delay as much as possible, limiting the big initial explosion recognized as "diesel knock" (actually a detonation in engineering terms).
Another problem with the extended ignition delay is that the more fuel introduced into the pre-combustion chamber during this period and the more heat of vaporization absorbed by the additional fuel, the more the bulk air temperature within the prechamber is reduced and the more the ignition delay is extended. These are the reasons for the requirement that the pre-combustion chamber be filled with as much air as possible at the highest temperature; two conditions which are hampered by the less than perfect pre-combustion chamber transfer holes at their discharge end into the pre-combustion chamber. One simple solution would be to increase the size of the transfer passages, but this would have repercussions in that it would require an increase in the diameter of the bottom of the pre-combustion chamber. This, in turn, would require a reduction in diameter of valve sizes and limit engine performance. Therefore, the only solution is to increase the coefficient of discharge of the transfer passages and, in effect, make them more aerodynamic and efficient.
It is also believed that the worst effect of the sharp-edged orifices of the transfer passages occurs during the pre-combustion chamber discharge; i.e. when the products of prechamber combustion, fuel and air still burning and the fuel in various stages of decomposition, are rapidly expelled from the pre-combustion chamber into the main combustion chamber. This process also expends pressure energy to induce velocity in the torch-like plumes. Since the kinetic energy generated by the velocity of the plumes is what induces the violent mixing and quick combustion of air in the main combustion chamber, it is desirable to accomplish this process as rapidly as possible with minimum pressure losses. I believe this process can also be expedited by improving the flow coefficient of the transfer passages. These passages were made divergent in the pre-combustion chamber design disclosed in my '744 patent referred to above so as to increase their discharge flow coefficient. However, their discharge flow coefficient can still be further improved by making the entrance to the passages, for the discharge function, more aerodynamic inside the bottom surface of the pre-combustion chamber.